Method For Reinforcing A Thermoplastic Resin Composition

ABSTRACT

The present invention is directed to plant fiber-reinforced thermoplastic compositions and a method for reinforcing thermoplastic resins. The present invention provides a use for the cellulose portion of a plant material, which is the portion left over after processing the selected plant materials to separate the hemi-cellulose and lignin from the cellulose.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of application Ser. No.13/648,738 filed Oct. 12, 2012.

FIELD OF THE DISCLOSURE

The present invention relates to a thermoplastic composite resincomposition which includes plant fibers and a method for reinforcingthermoplastic resin compositions. More particularly, the cellulosecomponent of plat material remaining after the removal of thehemi-cellulose and lignin components of the plant material is blendedwith one or more thermoplastic resins or to provide a reinforced resincomposite.

BACKGROUND OF THE DISCLOSURE

The plastics industry is one of the largest consumers of organic andinorganic fillers. Inorganic fillers such as calcium carbonate, talc,mica and the like are well known, as well as organic fillers such aswood flour, chaff and the like, fibrous materials such as asbestos andglass fiber, as well as graphite, cokes, blown asphalt, activatedcarbon, magnesium hydroxide, aluminum hydroxide and the like. All ofthese additives have high specific gravities and their ability toimprove physical properties of the composition is limited.

As an alternative to particulate fillers, thermoplastic materials canalso be formed with fibrous materials to overcome those deficiencies.Fiber-reinforced composite materials based on thermoplastic materialsare being increasingly used in many areas of technology in place ofmetallic materials as they promise a substantial reduction in weight,with mechanical characteristics which are otherwise comparable in manyrespects. For that purpose, besides the thermoplastic matrix, thesecomposite materials include a fibrous component which has a considerableinfluence on mechanical characteristics, in particular tensile andflexural strength as well as impact toughness of the composite material.Fibrous components used are (i) fibers of inorganic materials such asglass, carbon and boron, (ii) metallic fibers, for example of steel,aluminium and tungsten, (iii) synthetic organic fibers, for example ofaromatic polyamides, polyvinyl alcohols, polyesters, polyacrylates andpolyvinyl chloride, or (iv) fibers of natural origin, for example hempand flax.

The use of glass fiber-reinforced thermoplastic materials has ofparticular significance. In FIG. 1, a prior art process for theincorporation of glass fibers into a plastic resin, such aspolypropylene, is illustrated. The polypropylene 10 is initiallycombined at a suitable temperature and pressure with the glass fibers 12and other additives 14, as desired. The polypropylene 10, glass fibers12 and additives 14 are mixed to form the composite material 16. Thiscomposite material 16 can be subsequently extruded at 18 for use in aninjection molding process 20 to form a final molded product 22 havingproperties provided by the combination of the polypropylene 10 and glassfibers 12, along with any additional desired properties provided by theadditives 14.

However, the production of glass fibers requires the use of considerableamounts of energy and the basic materials are not biological in originso that the sustainability of the production process is open tocriticism from ecological points of view. Furthermore, the disposal ofglass fiber-reinforced thermoplastic materials is made difficult as evenupon thermal decomposition of the material, considerable amounts ofresidues are left, which generally can only be taken to a disposal site.Finally glass fibers involve a high level of abrasiveness so thatprocessing the materials in the context of usual processing methods forthermoplastic materials encounters difficulties.

Because of the above-mentioned disadvantages but also generally toimprove the material properties therefore at the present time there isan intensive search for possible ways of replacing the glass fiberswhich dominate in many technical uses, as a reinforcing component.Organic fibrous materials of natural origin, such as plant materialsappear to be particularly attractive in this connection because of theirlower density and the reduction in weight that this entails in thecomposite material as well as sustainability and easier disposal.

The potential of using natural or plant fibers in plastic applicationsas a substitute for synthetic fibers such as glass, carbon, nylon,polyester, etc. has been recognized. For example, Kolla et al. U.S. Pat.No. 6,133,348, which is hereby expressly incorporated by referenceherein, describes flax shives reinforced thermoplastic compositions anda method for reinforcing thermoplastic resins. The invention disclosedin Kolla provides a use for flax shives or particles in thethermoplastic compositions, which is the portion left over afterprocessing plant materials to separate plant fibers (bast fibers) fromthe shives. The shives are the core tissue fibers which remain after thebast fibers are removed from the flax stem via the mechanical separationprocess disclosed in Leduc et al. U.S. Pat. No. 5,906,030, or othermechanical separation processes involving the hammering or bending ofthe natural plant fibers. These core tissue fibers include thecellulose, hemi-cellulose and lignin components of the flax fiber, alongwith a smaller portion of the woody bast fibers that remain on theshives, giving the shives a fiber purity of approximately eightypercent, at maximum.

It will be noted however that the use of natural fibrous materials as afiber-reinforcing component can be confronted with worse mechanicalcharacteristics in the resulting composite materials, in comparison withfiber-reinforced composite materials with glass fiber constituents.Furthermore natural fibers such as flax, hemp or also wood particles areof a fluctuating composition: individual batches of the material differdepending on the respective cultivation area, cultivation period,storage and possibly preliminary treatment. That means however that themechanical characteristics of the fiber-reinforced thermoplasticmaterials to be produced also vary, which makes technical use thereofmore difficult. The material can further change in form and appearanceby virtue of progressing degradation processes. Finally, the constituentcomponents of the various natural fibers can themselves create issueswhen the fibers are utilized in this manner. In particular, thehemi-cellulose fraction of natural fibers absorbs moisture, causing adetrimental effect on the dimensional stability and water resistanceproperties of any thermoplastic material to which the natural fibers areadded.

As a result it is desirable to make use of the advantages linked to theuse of organic materials of natural origin in creating compositematerials, but by treating the natural fibers in a manner that improvesthe processing-relevant and use-relevant properties of the compositematerials.

SUMMARY OF THE DISCLOSURE

According to one aspect of the present disclosure, fibers of natural orplant materials are used in the filling and reinforcement of formedcomposite materials including the fibers and thermoplastic matrixresins, such as polyethylene and polypropylene. The natural plant fibermaterials to be used include cellulose, hemi-cellulose and lignincomponents or fractions. The fibers are treated prior to formation ofthe composite materials in order to separate the cellulose,hemi-cellulose and lignin fractions, such that the cellulose fraction orcomponent of the natural fiber can be chemically treated and removedfrom the hemi-cellulose and lignin fractions. The fibers of thecellulose component of the plant materials can be substituted for thesynthetic fibers used to at least achieve similar mechanicalcharacteristics for the composite material as when synthetic fibers areused, in particular the tensile and flexural strength as well as impacttoughness. In addition the use of the cellulose fraction of the naturalplant materials does not absorb and retain water, and thus does notdetrimentally affect the waterproof properties of the compositematerial. Further, the cellulose fraction of the natural plant componentenables the composite material to be readily disposed of and/orrecycled.

According to another aspect of the present disclosure, the natural plantfibers are mechanically treated prior to chemical treatment in order toobtain relatively pure plant material for use in the chemical extractionprocess. The particular mechanical treatment or decortication isaccomplished in a manner that reduces the break age of the core fibers,resulting in longer cellulose fibers from the chemical extractionprocess, that in turn provide a stronger composite composition withenhanced strength and lighter weight than glass fiber filled compositematerials.

Numerous additional objects, aspects and advantages of the presentinvention will be made apparent from the following detailed descriptiontaken together with the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the best mode of practicing the presentdisclosure.

In the drawings:

FIG. 1 is a schematic view of a prior art composite material productionprocess; and

FIG. 2 is a schematic view of a composite material production processaccording to the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring now to the drawing figures in which like reference numeralsdesignate like numerals throughout the disclosure, FIG. 2 illustrates aprocess for the formation of a product 116 created using a compositematerial 102.

The composite material 102 is formed of a thermoplastic resin ormaterial 104, which is the term used to denote polymer materials whichare soft or hard at the temperature of use and which have a flowtransitional range above the temperature of use. Thermoplastic resins ormaterials comprise straight or branched polymers which in principle arecapable of flow in the case of amorphous thermoplastic materials abovethe glass transition temperature (T_(g)) and in the case of (partly)crystalline thermoplastic materials above the melting temperature(T_(m)). They can be processed in the softened condition by pressing,extruding, injection moulding or other shaping processes to affordshaped and moulded parts. The thermoplastic material 104 used in thepresent disclosure can be any suitable thermoplastic resin material orcombination of multiple thermoplastic materials, such as a plasticincluding one or more natural or petroleum based thermoplastic resinssuch as polyethylene, polypropylene, polystyrene, polyvinyl chloride,polyacryl nitrite, polyamides, polyesters. polyacrylates and Poly LacticAcid (PLA), among others. The thermoplastic material does not have to bea homopolymer but can also be in the form of a copolymer, a polypolymer,a block polymer or a polymer modified in some other fashion.Polypropylene is a particularly useful thermoplastic material for use informing the composite material 102 of the present disclosure.

In addition to the thermoplastic material 104, the composite material102 includes cellulose fibers 106. These fibers 106 can be obtained fromany suitable natural plant material 109, such as natural fibrous plantmaterials including a) seed fiber plants, in particular linters, cotton,kapok and poplar down, b) bast fiber plants, in particular sclerenchymafibers, bamboo fibers, (stinging) nettles, hemp, jute, linen or flax(fibre flax and oil seed flax), and ramie, c) hard fiber plants, inparticular sisal, kenaf and manila, d) coir, and e) grasses. Bast fiberplants, such as flax and hemp, are particularly useful natural nonwoody, plant materials from which the cellulose fibers 106 can beobtained.

The bast plants include outer bast fibers that run longitudinally alongthe length of the plants and core tissue fibers disposed within theouter bast fibers. Because the core tissue fibers are the desiredfibers, the outer bast fibers must be removed prior to use of the corefibers. In removing the outer bast fibers, care must be taken to avoiddamaging or breaking the core tissue fibers in order to maximize thelength of the core tissue fibers. Thus in a first step the straw isratter under controlled environmental conditions (e.g., field ratted,chemically ratted and/or water rated) followed by mechanically treatingthe bast plant materials, in which the plant materials are decorticatedby shearing the bast fibers from the core tissue fibers, as opposed tohammering or bending/flexing the plant material as in priordecortication processes. By shearing the bast fibers from the coretissue fibers, the core fibers can be kept intact more readily, therebymaintaining the overall strength and length of the core fibers. Usingthis process, core fibers of approximately 95-98% purity can beobtained. In addition, both ratted and non-ratted plant material can beused in the decortications process to obtain a clean core tissue fiberthat can be used for production of the composite material.

In each case, the core fibers of the natural fibrous plant materials 109include cellulose, hemi-cellulose and lignin components. To obtain thecellulose fibers 106 utilized to form the composite material 102 fromthe natural plant material, the hemi-cellulose fraction 108 and ligninfraction 110 are separated from the cellulose fibers or fraction 106,such that a purified crystalline cellulose fraction 106 can be added tothe thermoplastic material 104 to form the composite material 102.

To separate the cellulose fibers/fraction 106 from the hemi-cellulosefraction 108 and lignin fraction 110 of the natural plant material 109,any suitable process 111 can be utilized, such as those employed onnatural plant materials 109 for paper pulping, e.g., soda or kraftpulping, among others. More specific examples of processes for theseparation of the hemi-cellulose fraction 108 and lignin fraction 110from the cellulose fibers 106 of the plant material 109 include thosethat utilize an alkaline material 113, examples of which are disclosedin Hansen et al. U.S. Patent Application Publication No. 2009/0306253and Costard U.S. Patent Application Publication No. 2010/0176354, amongothers, each of which are hereby expressly incorporated by referenceherein in their entirety.

One suitable example is an alkaline separation process shown in CostardU.S. Patent Application Publication No. 2010/0176354 where a naturalplant fiber material 109 is solubilized in an alkaline manner and whichis characterized in that the natural fiber material 109 is treated withan alkaline material 113 without being subjected to mechanical stress a)at a temperature of between 5 and 30° C. and then b) at a temperature ofbetween 80 and 150° C., and is then optionally washed and/or dried.

The alkaline materials 113 that can be used are, among other suitablealkaline materials, alkali metal hydroxide, in particular sodiumhydroxide or potassium hydroxide, alkali metal carbonates, in particularsodium carbonate or potassium carbonate, or alkali metal phosphates, inparticular trisodium phosphate or tripotassium phosphate.

The fiber degradation takes place at a pH of approximately between 8 to14, preferably 10 to 14. more preferably 11 to 12 in the cold process(step a)) and preferably at a temperature of between 10 and 30° C.,preferably between 10 and 25° C., in particular between 15 and 25° C.,more preferably between 15 and 20° C.

The cold treatment according to step a) takes place over a period of 10minutes to 3 hours, in particular 15 minutes to 2 hours and preferably30 minutes to 1 hour. The hot treatment used according to step b) of thenatural fiber material also takes place between a pH of 8 to 14,preferably 10 to 14, more preferably 11 to 12, and preferably at atemperature of between 80 and 140° C., preferably between and 140° C.,in particular between 90 and 135° C., more preferably between 100 and135° C.

The hot treatment according to step b) takes place preferably over aperiod of 20 minutes to 1.5 hours, in particular 30 minutes to 1 hourand preferably 45 minutes to 1 hour. The concentration of alkalinematerial in water in steps a) and/or b is, based on the activeingredient (typically a solid), preferably in the range from 5 to 15g/l, in particular 7 to 13 g/l, preferably 8 to 12 g/l, particularlypreferably at about 10 g/l.

The process performed according to steps a) and b) effectively dissolvesthe hemi-cellulose fraction 108 and lignin fraction 110 from the naturalplant material 109, which can subsequently be removed with the alkalinesolution, leaving the cellulose fraction 106 behind for subsequentwashing and drying to a desired moisture level, e.g., about 2% by weightor below.

The alkaline treatment according to the disclosure can be supported byadding excipients. Dispersants, complexers, sequestering agents and/orsurfactants are suitable here. Water glass and foam suppressors canlikewise optionally be used depending on the end-application. Othercustomary excipients can also be used. The addition of a complexer,dispersant and/or surfactant to the baths can accelerate and intensifythe wetting of the fibers. The materials customarily used for theserespective purposes in fiber treatment are suitable here.

When separated, the cellulose fibers 106 are at least 95% w/w purecellulose fibers, i.e., the fibers 106 contain not more than about 5weight percent of material other than cellulose, i.e., lignin andhemi-cellulose. Further, the cellulose fibers 106 have a mean fiberlength of less than about 2 mm.

Once liberated from the natural plant material 109, the cellulose fibers106 can be utilized to form the composite material 102. These fibers 106can be colored easily as the fibers 106 are very light, i.e., almostwhite in color and the composite made out of these is odorless. Chemicaltreatment of fiber 106 affects the cellulose structure, e.g., decreasingcrystallinity and increasing the amorphous structure. For example, thechemical treatment opens the bonds in the cellulose fraction or fibers106 for interaction with the polymer matrix 104 in forming thecomposites 102. The composite material 102 of the present disclosure maymixed together and processed by extrusion, compression molding,injection molding, or any other similar, suitable, or conventionalprocessing techniques for synthetic or natural biocomposites.

FIG. 2 shows one embodiment of the processing of the composite material102 of the present disclosure. The ingredients of the composite material102, i.e., a thermoplastic material 104 and the cellulose fibers 106,may be blended or compounded with one another in a manner effective forcompletely blending the cellulose fibers 106 with the thermoplasticmaterial 104, such as in a suitable mixer, e.g., a high or low intensitymixer. Depending upon the particular composition of the thermoplasticmaterial 104 and the cellulose fibers 106, the temperature of the mixerin one embodiment should be from about 140° C. to about 220° C. for theproper combination of the components to form the composite material. Oneexample of a mixer effective for blending the fibers 106 andthermoplastic material 104 is a high intensity thermokinetic mixer. Inthese types of mixers, frictional energy heats the contents until theybecome molten, a process that takes seconds or minutes depending on thespeed of the impeller. In another aspect of the invention, heat from anexternal source can be supplied to melt the thermoplastic material 104and effect blending of the cellulose fibers 106. An example of a lowintensity mixer is a ribbon blender.

The formulation of the composite material 102 can be tailored bymodifying the amounts or ratios of the thermoplastic material 104 andthe cellulose fibers 106 used to form the composite material 102depending on the particular application and/or function for thecomposite material 102. Additives (including, but not limited to, flowenhancers, anti-oxidants, plasticizers, UV-stabilizers, foaming agents,flame retardants, etc.) are used in formulation to enhance thefunctionality of the composite product. To accommodate the particularuse and corresponding required properties of the composite material 102,the blending of the polymers/thermoplastic material 104 and the fibers106 can also be varied in temperature and pressure. In addition, theblending parameters and component ratios for the composite material 102can be altered depending upon the particular pant material from whichthe fibers 106 are obtained. Examples of the polymers used as thematerial 104 include, but are not limited to acrylonitrile butadienestyrene, polyethylene, polypropylene, polystyrene, polyvinyl chloride,polyacryl nitrite, polyamides, polyesters, polyacrylates, otherengineering plastics and mixtures thereof.

In some particular embodiments of the composite material 102, the weightratios/percentages of the thermoplastic material 104 and the cellulosefibers 106 used in the formation of the composite material 102 rangefrom 1-60%. The fibre loading in biocomposite for the following processcan be varied from process to process. Exemplary fiber loadingpercentages according to various molding processes in which thebiocomposite material 102 is used are as follows:

Extrusion products: 1-30% (product examples: pies, profiles)

Injection molding: 1-45% (product examples: small components)

Compression molding: 1-60% (product examples: kitchen cabinets, bicyclecomponents)

Rotational molding: 1-30% (product examples: water tanks, large storageboxes)

Vaccuming forming/Thermoforming: 1-20% (product examples: packagingmaterials, cups, plates, boxes, building insulation)

In one particular embodiment, the mixing/extruding of the thermoplasticmaterial 104 and the cellulose fiber 106 to form the composite material102 is performed with a dry blender, mixer, parallel screw extruder. Theparallel screws in the device serve to blend the fibers 106homogeneously with the polymer 104, while also reducing the damageand/or breakage of the cellulose fibers 106 in the mixture forming thecomposite material 102. In addition, the parallel screws help to reducethe residence time of the composite material formulation 102 byincreasing the speed of mixing of the components of the compositematerial 102 in the device.

As a result of the use of purified cellulose fibers 106 obtained via themechanical and chemical processing described previously, the fibers 106develop a molecular bonding with the thermoplastic material 104 whenblended to form the composite material 102 which provides superiorperformance of to composite materials having only mechanical bindingbetween the polymer and the reinforcing fibers. Without wishing to bebound by any particular theory, it is believed that this molecularbonding occurs as a result of the thermoplastic material 104 flowinginto and filling the inside the modified fibers 106 during themixing/extrusion process. The increase in the melting temperature of thebiocomposite 102 indicates a possible polymerization effect of the fiberthat diffuses or dissolves into the polymer in the composite andcorrespondingly increases the thermal resistance of composite. Due tothe porous surface of the treated fiber, molten polymer matrix enters into the porous fiber and interlocks with each other and to form a strongbinding within the biocomposite 102. Further investigation is requiredto determine the exact nature of bond. In addition, polymer matrixesencapsulate the fibre and enhance the biocomposite strength and reducethe porosity and the formation of air pockets within the biocomposite.This molecular bonding between the fibers 106 and the thermoplasticmaterial 104 significantly improves the properties of the compositematerial 102, e.g., mechanical properties including tensile and flexuralstrength as well as impact toughness, and thermal properties. Theproperties of the biocomposite 102 vary as a result of the fibre loadingand the type of polymer and/or additives used in the formation of thebiocomposite 102. This, in turn, enhances the functionality of products122 formed of the composite material 102 and enable the products 122 tobe used in a wider range of industrial applications than priorfiber-reinforced materials. Also, in conjunction with the reduction inprocessing time in the parallel screw device, the molecular bondingbetween the fibers 106 and the polymer 104 limits any significantreduction of inbuilt additives present in polymer/thermoplastic material104. As a result, it is only necessary to supplement any requiredadditives, such as bonding additives, present in the polymer 104 duringthe formulation of the composite material 102, as opposed to adding theentire amount of the additives outside of those contained in the polymer104.

Once mixed/compounded, the melted composite material 102 can be allowedto cool to room temperature and then further processed by conventionalplastic processing technologies. Typically, the cooled blend isgranulated into fine particles. The fine particles are then utilized forextrusion 112, injection 114 and/or compression molding to form finishedparts or products 116.

In an alternative embodiment, the mixer can be operated without heat,such that the thermoplastic material 104 and cellulose fibers 106, afterbeing mixed together, are transferred to a feed hopper, such as agravity feed hopper or a hopper with a control feed mechanism.Alternatively, the thermoplastic material 104 and the cellulose fibers106 can be individually fed to the extruder without being previouslymixed together. The feed hopper transfers the composite to a heatedextruder 112.

The extruder 112 blends the ingredients under sufficient heat andpressure. Several well-known extruders may be used in the presentinvention, e.g., a twin screw extruder. The extruder 112 forces orinjects the composite material 102 into a mold 114. In an exemplaryembodiment, the flow rate of the extruder 112 may be between about 150and 600 pounds per hour. In other embodiments, the flow rate may behigher or lower depending on the type and size of the extruder 112. Theinjection mold 114 may be made up of one or more plates that allow thecomposite material 102 to bond and form a shaped-homogeneous product116. A typical plate may be made from hardened steel material, stainlesssteel material or other types of metals. A cooling system (e.g., aliquid bath or spray, an air cooling system, or a cryogenic coolingsystem) may follow the injection mold 114.

In the mixer, a number of optional processing aids or additives 115 canbe added to the thermoplastic material 104 and the cellulose fibers 106.These processing aids or modifiers act to improve the dispersion offibers 106 in the thermoplastic polymer material 104 and also helpfurther prevent the absorption of water into the fibers 106 and improvethe various thermal, mechanical and electrical properties of thecomposite material 102, e.g., the strength of the resulting compositematerial 102. The addition levels of the modifiers or compatibilizersused depends on the target properties. For example, where higher tensileand flexural strengths are desired, higher levels of modifier orcompatibilizer will be required. A compatibilizer is not required toachieve higher stiffness.

In one particular example of the present disclosure, the compositematerial 102 includes an amount of an wear additive 115 selected fromaluminium or copper powder, or combinations thereof to increase the wearproperties and enhance the longevity of the final product 122.

With regard to the molding processes 120 used to form the final product122, the composite material 102 improves the product 122 formed by theseprocesses 120 through the reduction of the formation of pin holes andthe porosity of the material product 122. Without wishing to be bound byany particular theory, it is believed that these results are achieved inthe composite material 102 as a result of the close packing andincreased density of the fibers 106, polymer 104 and additives 115 dueto the properties of the cellulose fibers 106, and the consequentremoval of entrapped air bubbles during the processing of the fibers 106and thermoplastic material 104. along with the additives 115, to formthe composite material 102. As a result, the final product 122 is moresolid and stronger than products formed from prior fiber-reinforcedmaterials.

Further, with the use of the cellulose fibers 106 formed in theabove-described manner, it is possible to achieve higher gradeproperties (mechanical, thermal, electrical, etc.) for the final product122 while using lower grade thermoplastic materials 104 in combinationwith the cellulose fibers 106. In particular, as a result of theproperties and purity of the cellulose fibers 106, the fibers 106 canbond well with a wide range of grade of polymeric/thermoplasticmaterials 104 to achieve products 122 with the desired properties.Further, to address any issues presented by the particularpolymer/thermoplastic material 104, the weight percentage or weightratio of the fibers 106 Fine can be increased in formulation ofcomposite material 104 without compromising the quality and desiredproperties of the final product 122. In addition, by increasing theamount of the cellulose fibers 106 utilized in the composite material102, the consequent consumption of the polymer 104 will be reduced.

For a better understanding of the objects and advantages of the presentinvention, the same will be now described by means of several examples.However, it should be understood that the invention is not limited tosuch specific examples, but other alterations may be contemplated withinthe scope and without departing from the spirit of the invention as setforth in the appended claims.

While the formulation of the particular biocomposite material 102depends on the final product 122 formed from the biocomposite material102, its functionality, and/or as described above the particular moldingprocess used to form the biocomposite material 102 into the finalproduct 122.

In one example of biocomposite composition 102, the formulationincludes:

a) natural/petroleum based thermoplastic material(s): 99-40% w/w

b) fiber 1-60% w/w

c) additives 1-5% w/w.

Biocomposite materials 102 of different grade (e.g., extrusion grade,injection grade, compression grade, rotational grade, vacuum forminggrade) are manufactured by changing the formulation of the biocompositematerial 102, and in one example by changing the amount of fiber 106present and consequently adjusting the percentages of the remainingcomponents.

One particular example of a thermoforming/vacuum forming formulation forthe biocomposite material 102 is as follows:

a) polystyrene

b) treated natural fiber

c) butane

d) additives (zinc stearate, magnesium stearate)

e) talcum powder.

Other examples of biocomposite material 102 formed according to thepresent disclosure are found in the following tables.

TABLE 1 Properties Liner low density polyethylene - dicumyl peroxidepre-treated flax fibre Flax straw/Industrial Hemp stalk ChemicallyComposite Unretted Field retted Water retted retted properties Unit FlaxHemp Flax Hemp Flax Hemp Flax Hemp Melt Flow g/10 min 2.8 2.6 3.7 3.54.1 3.4 3.8 3.5 Index Melting point ° C. 130 128 129 127.4 130.1 128130.6 129 Tensile Mpa 13.2 15.3 17.6 16.9 18.3 18.7 22.2 21 StrengthTensile Impact KJ/m² 178 172 188 182 194 178 223 205 strength HardnessSD 12 11 17 18 18 17 23 21 Water % 3-5 2-6 <1 <1 <1 <1 <1 <1absorption@50 RH

TABLE 2 Properties Liner low polyethylene - triethoxyvinylsilanepre-treated flax fibre Flax straw/Hemp stalk Chemically CompositeUnretted Field retted Water retted retted properties Unit Flax Hemp FlaxHemp Flax Hemp Flax Hemp Melt Flow g/10 min 2.0 2.2 2.7 2.4 2.6 2.4 2.82.4 Index Melting point ° C. 129 131.2 128.6 129 129 129 129 129.6Tensile Mpa 15 14.2 18.4 17.1 20.1 17.4 19.3 17.9 Strength at YieldTensile Impact KJ/m² 178 161 188 186 199 193 218 209 strength HardnessSD 9 11 14 15 19 19 20 18 Water % 3-5 2-6 <1 <1 <1 <1 <1 <1absorption@50 RH

TABLE 3 Properties High density polyethylene - benzoyl chloridepre-treated flax fibre Flax straw/Hemp stalk Chemically CompositeUnretted Field retted Water retted retted properties Unit Flax Hemp FlaxHemp Flax Hemp Flax Hemp Melt Flow g/10 min 1 1.2 1.6 1.5 1.8 1.7 1.81.4 Index Melting point ° C. 130 128 130 130 129 130 129 130 Tensile Mpa16.3 13.7 16.3 16.2 18 18.1 23.4 19.2 Strength at Yield Tensile ImpactKJ/m² 167 157 177 179 188 185 221 178 strength Hardness SD 17 11 12 1519 22 21 19 Water % 3 2 <1 <1 <1 <1 <1 <1 absorption@50 RH

TABLE 4 Properties High density polyethylene - dicumyl peroxidepre-treated flax fibre Flax straw/Hemp stalk Chemically CompositeUnretted Field retted Water retted retted properties Unit Flax Hemp FlaxHemp Flax Hemp Flax Hemp Melt Flow g/10 min 0.5 0.8 1.0 1.5 1.2 1.6 1.61.5 Index Melting point ° C. 130 126 131.6 128.4 128 129 129 128 TensileMpa 15 14.3 16.8 15.4 17.5 18.1 24.1 21.2 Strength at Yield TensileImpact KJ/m² 180 167 197 180 185 185 220 180 strength Hardness SD 13 914 12 15 12 17 15 Water % 3 2 <1 <1 <1 <1 <1 <1 absorption@50 RHOilseed flax and industrial hemp fiber has promising future in theplastic industries. It is observed that unretted and chemically retiedflax and hemp can be used in plastic composite (LLDPE and HDPE).Chemically retted fiber increased the T_(m) of composite compared topure polyethylene. The increase of T_(m) may be attributed to thepolymerization effect of the fiber that diffuses or dissolves into thepolymer in composite and increased the thermal resistance of composite.This investigation indicated that chemical retting has a great influenceon mechanical properties of (flax and hemp) polymer composites productsdeveloped through rotational molding processes.

Various other alternatives are contemplated is being within the scope ofthe following claims particularly pointing out and distinctly claimingthe subject matter regarded as the invention.

We claim:
 1. A method for reinforcing a thermoplastic resin compositioncomprising: a) providing an amount of cellulose fibers obtained by theseparation of the cellulose fiber fraction from hemi-cellulose andlignin fractions of a natural plant material; and b) blending from about1 to about 60 weight percent of the cellulose fibers based on the weightof the composition with a thermoplastic resin.
 2. The method of claim 1wherein the natural plant material is selected form the group consistingof natural fibrous plant materials including a) seed fiber plants, inparticular linters, cotton, kapok and poplar down, b) bast fiber plants,in particular sclerenchyma fiber plants, bamboo fiber plants, (stinging)nettles, hemp, jute, linen or flax, and ramie, c) hard fiber plants, inparticular sisal, kenaf and manila, d) coir, and e) grasses.
 3. Themethod of claim 1 wherein the cellulose fibers are formed of at least95% pure cellulose fibers.
 4. The method of claim 1 wherein thethermoplastic resin is selected from the group consisting ofpolyethylene, polypropylene, polystyrene, polyvinyl chloride, polyacrylnitrite, polyamides, polyesters, polyacrylates and mixtures thereof. 5.The method of claim 1 wherein the step of providing the cellulose fiberscomprises: a) mechanically separating core tissue fibers from outerplant fibers; and b) chemically separating the cellulose fibers fromhemi-cellulose and lignin fractions of the core tissue fibers.
 6. Themethod of claim 5 wherein the step of mechanically separating the outerplant fibers from the core tissue fibers comprises shearing the outerplant fibers from the core tissue fibers to minimize damage to the coretissue fibers.
 7. The method of claim 1 wherein the step of blending thecellulose fibers with the thermoplastic resin comprises mixing thecellulose fibers and the thermoplastic resin in parallel screw mixingdevice to minimize breakage of the cellulose fibers and the residencetime of the fibers and resin in the mixing device.
 8. The method ofclaim 1 wherein the step of blending the cellulose fibers with thethermoplastic resin comprises forming molecular bonds between thecellulose fibers and the thermoplastic resin.